There is a frequent requirement during a surgical procedure for suction in order to remove matter from the surgical site, whether it is tissue debris, smoke, fluid, gas bubbles or other unwanted matter that interfere with the procedure or obscure the surgeon's view of the surgical site. U.S. Pat. Nos. 6,210,405 & 6,482,202 describe examples of this type of surgical instrument, and embodiments of the present invention provide an improvement to such suction instruments.